I am looking for some clarification. I have been reading about installing an exhaust fan in a bathroom, and I have been reading that you should always vent to the outside, but I continue to read that you should never vent through the soffit.
I am not really sure what this means. Do they mean that you should not put the vent up to the soffit and hopes that it will go out, or do they mean that you should not even use a Soffit Vent designed for this.
I keep seeming devices like these Bathroom soffit vents and these which appear to be vents that get installed into the soffit, and then allow you to vent directly to the outside.

These devices seem like they would work, are these devices acceptable?

2 Answers
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A vent at the soffit can be done, but so could venting directly into the attic, and both are poor choices. This is because soffits are used for air intake into your attic (and out a ridge or gable vent). If you vent too close to the soffit, the warm moist air that you're trying to get out of your home will get sucked back up the soffit and into the attic, where it will cool and condense on the underside of your roof.

Agreed. A soffit vent is pretty much just the same as venting it directly into the attic. Either way, the moist warm air will be pulled up the underside of the sheathing looking for the ridge vent. (Yet it's incredibly common to see...including in the house I just put an offer on. ARGH!)
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DA01Apr 10 '12 at 2:44

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I also agree with BMitch. Venting through a soffit is often done, but this vent should be isolated from intake soffit vents by several feet at a minimum. It completely defeats the purpose if warm wet air is sucked right back in the attic by an adjacent soffit vent.
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shirlock homesApr 10 '12 at 10:09

I think the bigger issue here, is that DIYers see these types of products and think "Hey, I can use this to make my job easier!". The trouble is, just because they make the product does not mean it's applicable in all situations.

There may be situations where soffits are not used as vents, in which case these exhaust vents are perfectly acceptable. However, if your soffit is being used to vent the attic, you do not want to use one of these. The warm moist air will be sucked back into the attic, and you'll eventually run into problems.

One of the major difference between an amateur and a professional, is that a professional knows what products exist and when to use them. Whereas an amateur has a limited knowledge of available products, and adapts those products to meet their needs.

Minor nit-pick...I can't agree with the 3rd paragraph as being a truism. I've dealt with a lot of professionals that simply refuse to understand new products or modern building science practices and best methods (or even basic code updates). Maybe it's thanks to the internet, but a willing amateur who can spend some time doing serious research and reading can be very well informed compared to some professionals.
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DA01Apr 10 '12 at 14:15

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@DA01 I would argue that a "professional" that does not understand best practices, is no professional at all. Getting paid to do something should not be the only criteria for being called a professional.
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Tester101♦Apr 10 '12 at 14:21